The present invention relates to an electrophotographic image forming apparatus using a roller type charging system including a charge roller driven by a photoconductive element while contacting at least the image forming region of the element and applied with a DC constant voltage for uniformly charging the element, and roller cleaning means contacting the charge roller for removing toner and other impurities from the roller.
A roller type or contact type charging device including a charge roller contacting and driven by a photoconductive element for uniformly charging the element is extensively used in a copier, printer, facsimile apparatus or similar image forming apparatus. An electrophotographic image forming apparatus executes an electrophotographic process consisting of charging, exposure (optical writing), development, image transfer, paper separation, cleaning, and discharging. After the transfer of a toner image from the photoconductive element to a paper, toner left on the element is removed by a cleaning device together with paper dust and other impurities. Therefore, if the photoconductive element is completely cleaned by the cleaning device, theoretically no impurities including toner and paper dust will remain on the surface of the charge roller contacting the element. In practice, however, it is difficult to remove all the impurities from the surface of the photoconductive element. Should the impurities deposit on the charge roller, they would bring about irregular charging.
In light of the above, Japanese Patent Laid-Open Publication No. 2-272594, for example, teaches a cleaning arrangement wherein a sponge member is pressed against a charge roller for cleaning the roller. Japanese Patent Laid-Open Publication No. 5-265307, for example, discloses a cleaning arrangement wherein a cleaning member for cleaning a charge roller is slidable in the lengthwise direction of the roller.
However, the condition for maintaining the cleaning member in contact with the charge roller is delicate. Excessively weak contact would cause the cleaning effect to be practically lost. On the other hand, excessively strong contact would cause the surface of the charge roller to wear and reduce the life of the cleaning member. Assume that the cleaning member is constantly held in contact with the charge roller. Then, even if the above contact condition is adequate, filming occurs on the surface of the charge roller and lowers charge potential.
In order to obviate filming, an arrangement may be made such that the charge roller is movable into and out of contact with the photoconductive element or the cleaning member is movable into and out of contact with the charge roller, as taught in, e.g., Japanese Patent Laid-Open Publication No. 6-3930. In this arrangement, cleaning is effected as a part of a mechanical operation. This kind of scheme, however, needs a sophisticated mechanism and increases the cost of the apparatus.